The present invention relates to a new and improved construction of a machine for fabricating building boards or plates from a suspension of fibres and a curable material, and to an improved method of fabricating such building boards or plates.
Generally speaking, the machine of the present development is of the type containing an infeed line for the suspension and a movable band or belt for receiving thereon a layer of a mixture of fibres and the curable material formed from the suspension.
Building boards or plates, composed of a mixture of asbestos fibres and cement, are presently almost exclusively fabricated with machines containing a sieve cylinder which immerses within a container or vat containing the suspension. The aqueous suspension of the fibre material and the cement powder is dewatered due to a flow within the cylinder. The solid materials are retained at the surface of the cylinder and are removed therefrom by means of a felt band.
The prior art machines for fabricating the asbestos cement plates are afflicted with a spate of drawbacks. One of the most dominant ones of these is that a large proportion of the fine cement powder is entrained by the water flow through the sieve or screen of the sieve cylinder, and thus, is lost during the process of fabricating the plates. The fabricated plates therefore do not possess optimumly attainable strength values, especially have a poor ratio of strength in the transverse direction and lengthwise direction. The fibres are intensively aligned in the direction of rotation of the rotating sieve cylinder. Additionally, sieve or screen cylinders tend to become strongly contaminated, so that cleaning thereof is extremely complicated and time-consuming. The sieve or screen is a sensitive element and must be replaced within short time intervals.